1. The Field of the Invention
The invention relates to methods and systems for cleaning and sanitizing heating, ventilation, and air conditioning (HVAC) systems, including heat transfer coils.
2. The Relevant Technology
HVAC systems typically consume over 50% of a building's total energy. It is estimated that roughly half of this energy is wasted because the heat transfer coils in HVAC systems are operating in a fouled condition. Such fouled coils are the primary source of many operational problems found within HVAC systems, such as excessive equipment wear and tear, decreased human health due to poor indoor air quality, and excessive energy consumption. Hydrocarbon buildup from outside air pollution, pollen, dust, and grease are examples of common materials causing coil fouling.
Another common form of fouling arises from the formation of bacteria and fungi deep inside the coils. This biological form of fouling is exceptionally problematic for HVAC systems. When microbes take root deep inside the coils they begin to form biofilms, which is a plasticity type of membrane excreted by these micro-organisms. Biofilms are particularly detrimental to the HVAC system because these films are highly conductive which works to inhibit heat transfer between the metal surfaces of the coil and the passing air flow. In addition, biofilms can have sticky surfaces that can accumulate dust and the other fouling debris, thereby acting to inhibit air flow and efficient heat transfer though the coils.
When bacteria and fungi take root deep inside HVAC coils, many other operational problems can arise outside of inhibited air flow and heat transfer. As colonies of these microbes grow, their biological activity begins to off-gas noxious odors, creating a common problem in HVAC referred to as “Dirty Socks Syndrome”—a condition where the air supply in a building begins to present with a foul smell of dirty socks or other types of unpleasant smell.
For hospitals, biological fouling of HVAC coils is especially problematic and can present a near epidemic level problem for the global health care system. In the last several years, hospitals have seen a frightening rise of antibiotic resistant bacteria, such as Staph, MRSA, and others, taking root within nearly all medical facilities. It is now becoming a relatively common occurrence for sick patients to come into a medical facility needing treatment for one condition and then becoming infected with an antibiotic resistant strain of another illness contracted while visiting the hospital. In spite of extensive and vigilant sanitizing and cleaning efforts, medical facilities have so far been unable to eliminate dangerous microbes from the medical facility's operating environment. A major reason for this inability to eradicate dangerous microbes is due to the ability of antibiotic resistant microbes to hide, thrive, and migrate through the medical facility via its HVAC system. Specifically, it is deep inside the coils where antibiotic resistant microbes have found safe refuge, and the HVAC system provides means for traveling throughout the medical facility.
Cooling coils of HVAC systems within large medical facilities can range in depth from 6″ to 4 feet. Spacing between fins in the coils is extremely compact, with space measured in millimeters between each fin. The objective of the coils is to provide as much surface area as possible within a confined space, making the space between fins only large enough to permit air to pass through. In addition, the cooling coils in large facilities can often reach 15 feet in height and are sealed on top so that air can flow evenly through the coils. This means there is often no way to access coils from the sides or the tops of the system. The density of the packed coils serves to inhibit liquids from traveling more than 2 inches inside the coils, which leaves the vast majority of internal coil surface area completely inaccessible for cleaning.
The result is that internal surface area of HVAC cooling coils provide an ideal sanctuary for antibiotic resistant, and all other bacteria and fungi, to take root and thrive within a medical or other facility. Because the objective of the HVAC system is to circulate air throughout the facility, dangerous microbes can be carried in the air stream and efficiently spread throughout the facility. While a medical facility can be extremely vigilant in cleaning all exposed surface areas throughout the facility, the inability to sanitize and disinfect deep inside the coils leaves these facilities exposed and unable to fully mitigate dangerous risks posed by traveling microbes.
The standard practice employed throughout the HVAC industry, hotels, hospitals and other facilities is to clean HVAC coils using pressure washers. Another practice is to inject highly caustic or acidic solutions into the coils via a pressure washer or a hand held pump spray device. Yet another practice is to inject steam into the coils. These practices are completely ineffective in penetrating completely through the coils, especially coils deeper than 6 inches. These processes are also ineffective in removing biofilms or in sanitizing and disinfecting deep internal surface areas of the coils. In addition, all of these processes require complete shutdown of the air handler in order to service and are often damaging, wasteful, and hazardous to the environment.
Pressure washing, by far the most commonly employed practice in cleaning HVAC coils, involves the use of high pressure water, often exceeding 1,000 psi, to create a pressurized stream of water which is applied to the coil's outer surfaces. However, the dense packing of the coils acts to prevent water from penetrating more than about 2 inches into the coils, regardless of the injection of high pressure water. The tightly packed coils absorb the energy and deflect the pressurized water stream. In addition, due to weight of water and force of gravity, when the pressurized water stream loses kinetic energy due to absorption by the coils, the water naturally falls vertically towards the ground. Another weakness of pressure washing is that at 1,000+ psi the force of the pressurized water stream can quickly and easily bend the coil fins. The coils themselves are tightly packed and made from very thin soft metals, such as aluminum or copper. Once coils are bent and damaged in this manner, air flow is further restricted and made uneven, further reducing flow-through efficiency of the air handler. In addition, pressure washers utilize enormous quantities of water. Pressure washers can consume from 6-20 gallons per minute depending on their size. At the smallest version of 6 gallons per minute, a 1-hour cleaning of coils can result in the consumption of 360 gallons of water. It is not uncommon to consume well over 1,000 gallons of water during the cleaning of one large air handler.
Another technique for cleaning coils involves the use of a handle held pump spray and the direct injection of a caustic or acidic coil cleaner. This process is typically performed at lower pressure compared to high pressure washers. The idea behind caustic coils cleaners is to remove biofilm buildup inside the coils. Unfortunately, biofilms can present a plasticity type of membrane that is impervious to caustic, acidic, and even oxidizing solutions. In addition, caustic solutions can actively react with and strip layers of metal molecules from the coil surfaces. This is highly damaging and often leads to complete destruction of the coils over relatively short periods of service time. Finally, the pump spray method of injecting a caustic solution into coils experiences the same physical issues of pressure washing where only the surface and perhaps a few inches in depth are actually penetrated.
Another technique used to clean coils involves injecting the coils with high temperature steam. In this process, high temperature steam is directly injected into the coils with the hopes that the steam will physically break down biofilm, bacteria, dirt and grime. However, steam injection faces similar physical barriers as pressure washing because the outer coil surfaces can absorb kinetic and heat energy of the injected steam and inhibit its penetration to only a few inches. In addition, while steam may kill some of the bacteria and fungi near the outer coil surfaces, high temperatures are typically ineffective in removing the actual biofilm layer. In addition, the use of high temperature steam in many physical locations within a facility is impractical and can set up fire systems due to its excessive heat.
The ability to clean and sanitize cooling coils found in HVAC systems without damaging or shutting down the HVAC system is a solution that provides a whole new approach to significantly reduce energy consumption, reduce CO2 output, and greatly improve human health. To date, this process has been shown to improve the efficiency of commercial air handlers by up to 80%, which has been achieved by removing the fouling debris build up deep inside the coils. The HVAC system is also able to then greatly improve the volume of air moving through the air handler with less energy load. In addition, the innovation that will be outlined below is a scalable solution that is easy to apply and adopt, eliminates the need to invest in costly new capital equipment, and delivers its beneficial results immediately. This innovation is also a single platform solution that can be applied to any size or type of HVAC system and is equally effective if the HVAC system is a push or a pull type system. This means the blower within the air handler is pushing air through the coils or drawing air, via a reverse suction, of air flow. In addition, the described invention provides a means to deliver near perfect surface area coverage deep within the cooling coils that makes it possible to remove all biofilms, as well as eliminate any bacteria, fungi and other microorganisms that are found deep within HVAC coils and provide a highly effective and cost effective solution for medical facilities to quickly and effectively mitigate their antibiotic resistant microbe crisis by sanitizing and disinfecting the sole area within the medical facility (deep inside the coils) that is currently unreachable. Finally, this innovation is a truly sustainable solution. The process that will be described below uses roughly 95% less water than conventional methods of pressure washing, and no toxic, hazardous, or damaging chemicals. In addition, this solution is low pressure, making it impossible for the described process to deliver any damage to the HVAC coils.